Liquid-cooled fuel cell battery

ABSTRACT

The invention is directed to a battery with liquid cooling composed of at least two fuel cells that respectively comprise a negative pole plate, a membrane electrode unit and a positive pole plate that are connected to one another mechanically rigidly, gas-tight and electronically insulating by a frame element, whereby the battery is immersed into a coolant bath.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention is directed to a battery composed of at least two fuelcells that respectively comprise a negative pole plate, a membraneelectrode unit and a positive pole plate that are connected to oneanother in a mechanically rigidly, gas-tight and electronicallyinsulating manner by a frame element.

2. Description of the Related Art

Up to now, such batteries wherein every fuel cell of the batteryrespectively has a negative and a positive pole plate are disclosed, forexample, by German Letters Patent 44 42 285; however, the problem ofliquid cooling of such fuel batteries has not yet been solved. A liquidcoolant is desirable for stationary applications wherein the waste heatis to be utilized in order to keep the required heat exchanger and thedistribution of the heat compact.

Liquid-cooled fuel cell batteries are known that, however, respectivelycontain only individual contact or pole plates at the positive and atthe negative end of the battery. Within the battery, these individualcontact or pole plates are replaced by what are referred to as bipolarplates, which are often fashioned hollow. The liquid coolant of theknown liquid-cooled batteries is located in the cavities of the bipolarplates. Previously known bipolar plates adjoin, on the one hand, theanode space and, on the other hand, the cathode space of the individualfuel cells to be connected to one another. When a traditional battery isassembled, the bipolar plates are stacked on top of one another with themembrane electrode units of the individual fuel cells and aremechanically joined to one another by screw bolts, tie rods or otherclamp devices. A single pole or contact plate is then respectivelylocated at the end. This system is also referred to as filter presstechnique (see, for example, W. Vielstich from “Brennstoffelemente”,Verlag Chemie GmbH, pages 171 and 201/202).

A significant disadvantage of filter press technique is that very highdemands must be made of the edge seals of the fuel cell battery becausethe respective reaction agents, i.e. oxidant, fuel and coolant, must bereliably sealed from one another. Up to now, for example, an especiallyticklish, direct sealing without buffer area that must assure thatoxidant and fuel cannot overflow into one another is required at theedges of the bipolar plates. It is self-evident that such demands madeof the edge seals are reflected in the manufacturing costs of thebatteries. There is therefore a need to overcome the previously knownfilter press technique, not only given air-cooled fuel cells as in theabove-cited German Letters Patent 44 42 285, but also givenliquid-cooled fuel cell batteries.

SUMMARY OF THE INVENTION

It is therefore an object of the present invention to make aliquid-cooled battery of fuel cells available that is designed withoutdirect edge sealing between cathode and anode space.

The general perception of the invention is that this is possible givenemployment of individual sealing of the fuel cell units of a batterydisclosed by German Letters Patent 44 42 285 when a battery manufacturedtherefrom is immersed into a coolant bath.

The subject matter of the invention is a battery with liquid coolingcomposed of at least two fuel cells that respectively comprise anegative pole plate, a membrane electrode unit and a positive pole platethat are connected to one another mechanically rigidly, gas-tight andelectronically insulating by a frame element, whereby the battery isimmersed into a coolant bath.

A further subject matter of the present invention is a method forcooling a fuel cell battery, whereby the battery is cooled by immersioninto a coolant bath.

In one embodiment of the invention and of the inventive method, thebattery is completely immersed into a coolant bath.

In an advantageous development of the invention, the container for thecoolant bath is integrated such in the battery housing that the batteryhousing itself is no longer surrounded by liquid coolant.

The electrolyte membrane, which is the heart of the membrane electrodeunit of the fuel cell, extends up to the edge of the cell and could bewashed out given employment of water as coolant. It is thereforeprovided in an advantageous development of the invention that it is notwater but a hydrophobic, i.e. water-repellant coolant (for example, oilor transformer oil that does not wet the membrane that is employed.Alternatively to this advantageous embodiment, the electrolyte membranecan be prevented from being washed out by water as coolant in that aseal as offered, for example, by the Gore company in conjunction withthe membrane electrolyte unit and that precludes this washing effect isemployed in the individual sealing of the membrane electrode unit by theframe element. The costs of a battery constructed in this waynonetheless still lie below the costs for the seals of the known bipolarplates.

It is advantageous when the coolant flows through the coolant bath. Theflow can thereby be effected solely by convection. As needed, the flowcan also be generated by a pump or the convection can be intensified bya pump.

It is advantageous when the flow existing in the coolant bath isregulated such that it is uniformly distributed over the entire fuelcell battery. This can occur via a coolant distributor.

In an advantageous development of the method, the flow velocities and/orthe flow distribution of the coolant in the coolant bath can beregulated. This is especially practical when the battery is intended tomeet different power demands and has a differing cooling need over timeas a result thereof.

What is referred to here as “battery” is an aggregate or stack of atleast two senies-connected, individual fuel cells. One possibleapplication of such a battery is, for example, decentralized powergenerating wherein aggregates having a far higher plurality ofindividual fuel cells are employed. For example, a battery must producea power of approximately 10 kW for employment in a household energysupply system for a single-family house. Given an assumed cell area ofapproximately 300 cm² and a power of approximately 100 Watts perindividual fuel cell, a battery employable therein comes out to about100 individual cells.

The fuel cells that are disclosed in the above-cited German LettersPatent 44 42 285 are preferably referred to here as “individual fuelcell” or “fuel cell unit”. The full content of this Letters Patent isherewith referenced and the entire disclosure thereof is included in thesubject matter of the present specification. Said fuel cells are unitsthat can be individually handled and that respectively comprise anegative pole plate, a membrane electrode unit and a positive poleplate, whereby the aforementioned component parts are connected to oneanother mechanically fairly, gas-tight and electronically insulating bya respective frame element.

What is referred to here as “membrane electrode unit” is a membranerespectively having a negative and a positive electrode. All such unitsthat are standard in this technology are included under the term“membrane electrode unit”. The electrodes preferably do not extend up tothe edge of the membrane but leave an edge area of the membrane free, sothat a frame element of the fuel cell embraces only the positive andnegative pole plate of the fuel cell as well as the membrane itself.

What is fundamentally referred to as “frame element” is that part thatis suitable for connecting at least negative pole plate, membrane andpositive pole plate and, potentially, the electrodes or other componentparts of the fuel cell as well to one another mechanically firmly,gas-tight and electronically insulating. The frame element can becomposed of one piece; however, it can also be composed, for example, ofa plurality of parts. The frame element preferably has a U-profile crosssection, whereby the two U-legs press the two pole plates together withthe membrane and thus close off the inside of this unit gas-tight fromthe penetration of gasses. The frame element corresponds to the frameelement that was disclosed in the afore-mentioned German Letters Patent44 42 285.

Each of the fuel cells preferably has at least four through supply andwaste disposal openings that are respectively connected to one anotherwithin a battery.

When stacking at least two inventive fuel cells to form a battery, adirect mechanical and electronic contact of the negative pole plate ofthe one fuel cell with the positive pole plate of the next fuel cellpreferably derives. The two cells are thus electrically connected inseries. When present, the direct mechanical and electronic contactoccurs along the four supply and waste disposal openings. The negativeand positive pole plates of the two fuel cells adjoining one another arethereby shaped such that an interspace or cavity through which coolantcan flow remains between the completely stacked fuel cells that are indirect mechanical and electronic contact.

Upon immersion of the battery or of the fuel cell stack into a coolantbath, for example, the coolant flows through these cavities. The flow ofthe liquid coolant then proceeds analogous to the air stream in themainly air-cooled version of a fuel cell battery that is known from theabove-cited Letters Patent.

The flow velocity in the coolant bath can be regulated via a pump. Givenfluids with high heat capacity, a slight flow velocity already sufficesin order to achieve a good cooling effect. Turbulences that aregenerated in the stream of the coolant are advantageous because the heatcapacity of the coolant, which is not substrate-specific, is thusincreased. In this context, the application having Ser. No. 19635901.5is referenced, the technical teaching thereof being suitable foremployment in the scope of the present invention.

The flow distribution can be regulated by a coolant distributor that isattached to the admission of the liquid coolant and that divides theuniform stream of coolant at the admission. The coolant distributorserves the purpose of uniformly supplying the fuel cell battery withcoolant.

The flow velocity of the coolant within the liquid and coolant bath canbe regulated by the pump and the flow distribution.

What is meant by “hydrophobic” is the property of a medium to have awater-repellant effect. All the coolants that do not dissolve in water,i.e. are not suitable for wetting the water-saturated membrane andthereby washing it out, are understood by a hydrophobic coolant

The pump with which the flow of the coolant is potentially intensifiedcan be an arbitrary pump with which the liquid can be suctioned in,placed under pressure or compressed such that a flow arises. Thearrangement of the pump in the overall system is arbitrary and can bothprecede as well as follow the actual coolant bath.

The coolant bath is situated in a liquid-light container. This ispreferably provided with at least two permanent openings, one at theadmission and one at the discharge of the coolant. However, it cancomprise many openings; a coolant distributor is then usuallysuperfluous.

In an embodiment, the present invention provides a liquid cooled batterythat comprises at least two fuel cells, each fuel cell comprising anegative pole plate, a membrane electrode unit and a positive poleplate. The fuel cells are connected to one another by a mechanicallyrigidly, gas type in an electronically insulating manner by a frameelement. The frame element accommodates a coolant bath in which thecells are at least partially immersed. The frame element furthercomprises a coolant inlet and a coolant outlet whereby coolant flowsthrough the coolant inlet, around the fuel cells and out the coolantoutlet.

In an embodiment, the fuel cells are completely immersed in the coolantbath.

In an embodiment, the coolant is a hydrophobic coolant.

In an embodiment, the battery further comprises a pump for pumpingcoolant through the frame element.

In an embodiment, the frame element further comprises a coolantdistributor connected to the coolant inlet.

In an embodiment, the frame element further comprises two opposingsidewalls. The fuel cells are sandwiched between the two opposing sidewalls. One of the sidewall comprises a coolant inlet as well as acoolant distributor and the other of the sidewalls comprises a coolantoutput.

In an embodiment, the present invention provides a method for cooling acell fuel battery that comprises the steps of providing a battery asdescribed above, and providing a flow of coolant through the coolantinlet, around the fuel cells and out the coolant outlet.

Other objects and advantages of the present invention will becomeapparent from reading the following detailed descriptions and appendedclaims, and upon reference to the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates the embodiment of the inventive battery wherein thecontainer for the coolant bath is integrated into the battery housing.

FIG. 2 illustrates the embodiment of the inventive battery wherein theflow in the coolant bath is distributed via a coolant distributor.

It should be understood that the drawings are not necessarily to scaleand that the embodiments are sometimes illustrated by graphic symbols,phantom lines, diagrammatic representations and fragmentary views. Incertain instances, details which are not necessary for an understandingof the present invention or which render other details difficult toperceive may have been omitted. It should be understood, of course thatthe invention is not necessarily limited to the particular embodimentsillustrated herein.

FIG. 1 shows the illustration of an inventive battery composed of astack of individual fuel cells 1 respectively forming a unit that can behandled, this having four through supply or waste disposal openings 2 a,2 b, 2 c and 2 d. The battery is surrounded by a six-sided,cuboid-shaped battery housing. FIG. 1 shows the battery before assembly,the direction thereof being indicated by the arrows 7. The assembly canensue with any fluid-tight connection of the two parts.

The upper side 3 (FIG. 2) of the battery housing with the two currenttaps 4 a and 4 b as well as the side 5 of the battery housing with theend and supply openings 2 a through 2 d can be seen in the upper half ofFIG. 1. The stack of fuel cells 1 is held together, for example, byscrew closures or tie rods 13 that, again by way of example, areadjusted via a screw thread at the upper side 3 and the underside (notshown). The end 5 and supply openings 2 a through 2 d are connected toaxial channels that extend over the entire cell stack

During operation of the battery, the oxidant, for example, is deliveredvia the supply opening 2 b and is then conducted through the adjoiningaxial channel through the entire fuel cell stack of the battery, havingrespective openings to the individual cathode spaces. The oxidantconsumed in the individual cathode spaces of the battery can in turnleave the cell stack through the waste disposal opening 2C via thelikewise through waste disposal channel. In the aforementioned example,the fuel is then correspondingly supplied via the supply opening 2 a andeliminated via the waste disposal opening 2 d.

The diffusors 6 a with whose assistance the coolant can be distributedin the coolant bath are shown transverse to the cell stack Theattachment of the diffusers is not absolutely required but can becontained in the battery or not respectively as needed and dependent onthe embodiment of the invention.

Upon assembly of the battery, the upper half of FIG. 1 is plugged intothe lower half of FIG. 1, as indicated by the arrows 7, whereby theedges of sides 3 and 5 of the battery housing meet the seal surface 8along the adjoining edges of the battery housing that is shown in thelower half of FIG. 1. The seal surface 8 assures that the container isliquid-tight.

The admission opening 11 and the discharge opening 12 of the coolant canbe seen at the two sides 9 and 10 of the liquid container and batteryhousing. Either the admission opening 11 or the discharge opening 12 maybe connected to a coolant pump 21. Imnediately adjoining the admissionopening 11, the battery housing has more diffusers 6b that residetransverse to the diffusors 6 a that are shown in the upper half of FIG.1. As already mentioned, the diffusors 6 a help for uniform distributionof the coolant in the coolant bath. The attitude of the diffusors 6 a isthereby arbitrary and FIG. 1 shows an exemplary arrangement.

The fat that the battery is shown as cuboid and, thus, six-sided in bothFIGS. 1 and 2 merely serves for simplification and illustration of theinventive battery. This development is in fact a preferred embodiment,but the invention is definitely not limited to this shape of thebattery, on the contrary, it can also cover all types of batteries indifferent geometrical shapes.

FIG. 2 shows a development of the invention with a coolant distributor.The coolant distributor is thereby integrated such in the batteryhousing that a more compact structure is achieved. The middle of FIG. 2again shows the stack of individual fuel cells 1 with which the batteryis constructed. One can likewise see the front surface 5 of the batteryhousing with the four waste disposal and supply openings 2 a, 2 b, 2 cand 2 d through which the reaction gasses are conducted through the fuelcell stack and through which the consumed reaction gasses are eliminatedfrom the battery cell stack The current tap 4 is likewise situated atthe side 5 of the cuboid and, therefore, six-sided battery.

At its edge directed toward the front, the side 10 of the battery showsthe coolant admission opening 11. A coolant distributor is integratedsuch into tis side 10 of the battery shown in FIG. 2 that the coolantflows into the fuel cell stack 1 through the various openings 1 a thatare located at the inside at this side. The openings 11 a of thedistributor are designed such that the coolant experiences an optimallyuniform distribution along the entire fuel cell stack At its outwardlydirected edge, side 9 of the battery shown in FIG. 2 again exhibits thecoolant discharge opening 12 through which the used coolant in turnleaves the coolant bath in which the battery is immersed. The inside ofthe side 9 of the inventive battery housing that is shown in FIG. 2cannot be seen and this, byway of example and not necessarily, has thesame distribution of openings 11 a, which serve as outlet, as the side10. Finally, how the battery is assembled is also indicated in FIG. 2 bythe four arrows 7.

It should be reemphasized that the FIGS. 1 and 2 merely describepreferred embodiments of the inventive battery and are definitely notintended to limit the scope of the application, particularly withrespect to their geometrical illustration, which is highly simplified.On the contrary, the present invention is not bound to any kind ofgeometrical fashioning but is quite generally applicable to batteriescomposed of fuel cells wherein the individual fuel cells represent unitsthat can be individually handled and that can be adequately cooled byimmersion into a coolant bath, potentially with appertining flow of theliquid located in the coolant bath. In particular, the inventive batterycan forego the especially problematical seals between cathode and anodespace, as already mentioned above.

Inventively, the battery housing or the coolant bath into which thebattery is partly or completely immersed for cooling is fashioned suchthat a testing of the fuel cell stack as well as a testing of theindividual gas conduits is possible during operation, i.e. given ongoingcooling, so that, for example, faulty cells or leaks can be found andthe faults can be eliminated while the battery is in the coolant bath.Since all seals of the reaction gas spaces in the above-cited GermanLetters Patent 44 42 285 lead into the exterior space, which representsthe coolant bath in this case, namely, all gas leaks can be easilydetected on the basis of the emerging gas bubbles. Since the cells canbe made individually easily accessible in the disclosed battery design,there is also a possibility of detecting faulty cells on the basis of asimple voltage measurement.

From the above description, it is apparent that the objects of thepresent invention has been achieved. While only certain embodiments havebeen set forth, alternative embodiments and various modifications willbe apparent from the above descriptions to those skilled in the art.These and other alternatives are considered equivalents and within thespirit and scope of the present invention.

What is claimed is:
 1. A liquid cooled battery comprising: at least twofuel cells, each fuel cell comprising a negative pole plate, a membraneelectrode unit and a positive pole plate, a frame element connecting thefuel cells to one another with a mechanically rigid and gas-tightconnection with each cell being electronically insulated from the othercells, the frame element accommodating a coolant bath in which the fuelcells are at least partially immersed, the frame element having acoolant inlet and a coolant outlet, and a pump for pumping the coolantinto the coolant inlet, around the fuel cells and out the coolant outletwith the frame element working as a distributor for the coolant beingpumped by the pump.
 2. The battery according to claim 1, wherein thefuel cells are completely immersed in the coolant bath.
 3. The batteryaccording to claim 1, wherein the coolant is a hydrophobic coolant.
 4. Aliquid cooled battery comprising: at least two fuel cells, each fuelcell comprising a negative pole plate, a membrane electrode unit and apositive pole plate, a frame element connecting the fuel cells to oneanother with a mechanically rigid and gas-tight connection with eachcell being electronically insulated, the frame element comprising twoopposing sidewalls, the fuel cells being sandwiched between the twoopposing side walls, the frame element defining a coolant bath in whichthe fuel cells are at least partially immersed, one of the opposingsidewalls of the frame element comprising a coolant inlet and a coolantdistributor, and the other of the sidewalls of the frame elementcomprising a coolant outlet; and a pump connected to the coolant inletfor pumping coolant through the frame element so that coolant flowsthrough the coolant inlet through the coolant distributor, around thefuel cells and out the coolant outlet.
 5. The battery according to claim4, wherein the fuel cells are completely immersed in the coolant bath.6. The battery according to claim 4, wherein the coolant is ahydrophobic coolant.